[CSS Grid Layout] Increase coverage for first-line pseudo-element

Add missing cases checking that first-line pseudo-element from ancestors
is ignored inside the grid.

TEST=fast/css-grid-layout/grid-container-ignore-first-line.html

BUG=395788

Review URL: https://codereview.chromium.org/702663002

git-svn-id: svn://svn.chromium.org/blink/trunk@184885 bbb929c8-8fbe-4397-9dbb-9b2b20218538